1. Field of the Invention
The present invention generally relates to viewfinders and, more particularly, is directed to an electronic viewfinder which displays thereon a video image information from an image pickup element.
2. Description of the Prior Art
Recently, a silver salt film camera having an electronic viewfinder has been proposed, in which an incident light from a camera lens is imaged on a silver salt film and on an image pickup element and a video image information from the image pickup element is monitored by a display apparatus.
According to this electronic viewfinder, video image informations concerning the normal photographing except multiple exposure photographing can be monitored by a display apparatus, which is convenient for a cameraman to confirm the video image data after the picture is taken.
However, when the cameraman utilizes the salt film camera having the above-described electronic viewfinder and reduces exposure per picture to take a picture in the multiple exposure mode where a plurality of video images are overlapped, there is then the following problem. That is, a latitude of the image pickup element is about 1/3 of that of the silver salt film so that, when a picture taken in the multiple exposure mode is displayed by the electronic viewfinder using an image pickup element, a picture portion on the low brightness side is darkened. On the other hand, if the latitude of the low brightness side is matched with that of the silver salt film, this time, a picture portion on the high brightness side is saturated and whitened. A phenomenon in which a picture is partly or wholly whitened or darkened due to extreme difference of brightness will be hereinafter referred to as a deteriorated picture.
Therefore, in the electronic viewfinder, in order to prevent the picture portion on the low brightness side from being produced as the deteriorated picture, it is proposed that an automatic gain control (AGC) section is provided to increase a gain of the low brightness side for adjusting the brightness. This proposal, however, encounters with a problem such that if the gain of the low brightness side is increased, a noise also is amplified to cause the image quality of the picture to be deteriorated. Further, if a means for avoiding the deteriorated picture on the low brightness side is realized by an electronic circuit, there is the disadvantage that the circuit arrangement thereof is complicated.